1. Field of the Invention
The present invention pertains to fluid supplies for fuel processors, and, more particularly, to a fluid balance control system for use in a fuel processor.
2. Description of the Related Art
Fuel cell technology is an alternative energy source for more conventional energy sources employing the combustion of fossil fuels. A fuel cell typically produces electricity, water, and heat from a fuel and oxygen. More particularly, fuel cells provide electricity from chemical oxidation-reduction reactions and possess significant advantages over other forms of power generation in terms of cleanliness and efficiency. Typically, fuel cells employ hydrogen as the fuel and oxygen as the oxidizing agent. The power generation is proportional to the consumption rate of the reactants.
A significant disadvantage which inhibits the wider use of fuel cells is the lack of a widespread hydrogen infrastructure. Hydrogen has a relatively low volumetric energy density and is more difficult to store and transport than the hydrocarbon fuels currently used in most power generation systems. One way to overcome this difficulty is the use of “fuel processors” or “reformers” to convert the hydrocarbons to a hydrogen rich gas stream, commonly referred to as “reformate”, which can be used as a feed for fuel cells. Hydrocarbon-based fuels, such as natural gas, LPG, gasoline, and diesel, require conversion processes to be used as fuel sources for most fuel cells. Current art uses multi-step processes combining an initial conversion process with several clean-up processes. The initial process is most often steam reforming (“SR”), autothermal reforming (“ATR”), catalytic partial oxidation (“CPOX”), or non-catalytic partial oxidation (“POX”). The clean-up processes are usually comprised of a combination of desulfurization, high temperature water-gas shift, low temperature water-gas shift, selective CO oxidation, or selective CO methanation. Alternative processes include hydrogen selective membrane reactors and filters.
Thus, many types of fuels can be used; some of them hybrids with fossil fuels, but the ideal fuel is hydrogen. If the fuel is, for instance, hydrogen, then the combustion is very clean and, as a practical matter, only the water is left after the dissipation and/or consumption of the heat and the consumption of the electricity. Most readily available fuels (e.g., natural gas, propane and gasoline) and even the less common ones (e.g., methanol and ethanol) include hydrogen in their molecular structure. Some fuel cell implementations therefore employ a “fuel processor” that processes a particular fuel to produce a reformate stream used to fuel the fuel cell.
The handling of fluids is consequently an important component of fuel processor design. Typically, for instance, several aspects of the fuel processor's operation require a supply of air. Fuel processors therefore frequently have an air supply that feeds air to the parts of the fuel processor needing air. In a typical single-source air supply system, air coming off of a compression device (blower or compressor) is split up to deliver fractions of the supply to various sub-units within the fuel processor. Each air line branching off to each sub-unit is metered and monitored by a flow controller and flow meter or a combination of both in one unit. However, in this configuration, the upstream pressure of the flow controllers (downstream pressure of the compression device) fluctuates when the controllers are opening and closing. As a result, the flows fluctuate, causing an undesirable imbalance in air to fuel ratio. The imbalance causes inconsistency in air flows to the various downstream sub-units, potentially causing upset conditions. Some approaches try to remedy this effect by providing independent air sources for each of the sub-units. However, this leads to more costly components, complicated control schemes, and increased potential breakdown of additional components. Still others have used orifice plates to meter flow to various units. This tends to make the design complicated as orifice plates have to be adjusted once the air demands change. Similar problems are encountered with the handling of other fluids.
The present invention is directed to resolving, or at least reducing, one or all of the problems mentioned above.